WIP: when trying to repair a chunk, do not consider offline hosts as healthy

~~The code for the health loop determining the health of a chunk and the repair loop determining the health of a chunk are different. The biggest difference is that one considered offline hosts to be unhealthy, and the other did not.

This MR does a quick patch to fix the discrepancy, though really this code should probably be refactored so that both the health loop code and the repair loop code are using the same implementation to figure out the health of chunks.

We should probably merge this with the expectation of returning to it soon.~~

Going to break this down a bunch and open a bunch of separate MRs.